1. The Field of the Invention
This invention relates to the field of data association, correlation and routing in industrial processes.
2. The Relevant Technology
In automated industrial processes and systems, one often encounters situations in which it is necessary to establish a temporal correspondence between data received from several different data sources. In one such type of system, it is necessary to make an accurate association between parameter data and position data. So, for example, in a production-line context, it may be important for ongoing control of the production process to know precisely where on the line a workpiece was when a given parameter, say workpiece length, was measured.
There have been several techniques previously developed for associating and establishing a temporal correspondence between different types of data. For any data correlation to be possible, each type of data to be correlated with other data must include not only parameter identification and measurement values, but also address or associative information that enables a correlator or comparator (typically a microprocessor) to identify the two or more data items that are to be correlated. Preferably the correlator should establish a linked data association that, as a correlated data record, can be utilized elsewhere in the production process.
However, earlier techniques for associating position data with parameter data have encountered problems with the system architecture and have furthermore often not been determinative; that is, these techniques do not provide certainty that one type of parameter data is correctly grouped with a second type of parameter data.
In one previously known type of system, the input/output data interfaces of a series of parameter-sensing devices accepting electronic data inputs and providing electronic data outputs are bussed together linearly. In telecommunication nomenclature, this is referred to as a multidrop configuration. Generally, a multidrop configuration has a communication host (such as a sensor polling unit) which sequentially requests readings from each node on the network. At one end of this bus, a sensor polling unit is connected for transmitting data to and receiving instructions from each parameter-sensing device. The sensor polling unit is coupled to and user-operable by means of a host computer. In such a system, a position-sensing device is not connected to the sensor polling unit. Instead, the position-sensing device is connected to the host computer by means of a separate connection.
The foregoing technique suffers from two problems. Because the parameter-sensing devices are strung together on a single bus, the sensor polling unit can transmit data to and receive data only from a single parameter-sensing device at any given time. Specifically, since all nodes share the same response channel only one node can respond at a time. The time to turn around a request/response transaction is limited by the response channel bandwidth, specifically the response message (sensor reading) and overhead, back to the host. Channel bandwidth is a function of a number of factors, including physical distance between sensor and data poller. Furthermore, the host systems architecture is often not optimized to allow full utilization of the bandwidth. Response messages received from the sensor are normally signalled to the processor via an interrupt which may not be serviced until such time as other higher priority tasks have completed. During this time, the communications channel can be idle.
That means the multidrop technique tends to be too slow for the speeds and degrees of accuracy needed in many industrial processes, since more than one sensing device may be competing for data input or output, and by the time a given device has access to the sensor polling unit, the workpiece (say) may have moved downstream in the production line (say) by a distance that renders the data no longer sufficiently accurate or meaningful to be correlated from a workpiece position viewpoint with subsequent processing steps required to be made on the workpiece. Furthermore, if even a single parameter-sensing device is not functioning properly, the entire system can falter and the operator must check each node along the line to determine the source of the problem.
The second problem associated with the foregoing technique is that since the position data are acquired by the host computer by means of a connection separate from that for parameter data, the association of the two types of parameter data performed by the host computer is non-determinative—in other words, the operator cannot be sure whether parameter data measured during some interval of time or at some point or region of space is accurately correlated with position data purportedly relating to that particular interval of time or region of space. Since position data and parameter data are transmitted to the host computer by means of two separate connections, if position data is improperly synchronized with data received from a parameter-sensing device via the sensor polling unit, the position data may be imperfectly correlated with parameter data. The system may be tolerant of minor discrepancies between parameter data and supposedly associated second type of parameter data, but as production line speeds increase and as tolerances become more critical, such discrepancies are less tolerable and can cause production of out-of-specification rejects, or other serious problems.
Another type of previously known system used for data association uses an architecture that busses together parameter-sensing devices by means of a star network; each parameter-sensing device has a direct connection to the sensor polling unit. In this way, if a single parameter-sensing device is not operating correctly, the sensor polling unit need not be prevented from communicating with the remainder of the nodes on the network, and the entire system need not falter in the event of failure of a sensing device.
Nevertheless, this set-up is still less than ideal. In the star network, sensor data from multiple sensing devices are transmitted to a single sensor polling unit which, after grouping or otherwise assembling data, is used to transmit these data over an Ethernet connection to a host computer; however, position data is transmitted to the host computer by means of a separate connection. As before in the multidrop configuration, this system does not address correlation problems; there may still exist an imperfect association between parameter data and the two types of parameter data. If the data signal received from the sensor polling unit cannot reliably be correlated with a particular interval of time or region of space, then the received signal may be seriously corrupted or even useless to the purpose at hand.
A satisfactory solution for associating two or more types of parameter data is not found in known techniques. A satisfactory device to associate and correlate data, especially parameter data with position data should:                (a) establish a temporal correspondence between the two types of parameter data;        (b) be very fast, such that the temporal correspondence is sufficiently precise as to be useful as an input to downstream process control or monitoring device in the production line (say) or other industrial process;        (c) be adaptable to different types of parameter-sensing devices.        
The aforementioned desirable characteristics of a sensor concentrating unit not currently met by the known art may be realized by directing both types of parameter data first to the sensor concentrating unit, at which point the sensor concentrating unit correlates given one type of parameter data with a second type of parameter data. The two types of parameter data can be coupled using an accompanying data tag identifying the associated data. The associated data and data tag can then be packeted and routed to the microprocessor or PC for subsequent processing, or else sent directly downstream to a process controller.